1. Field of the Invention
The present invention relates to a boot, which is installed to rack-and-pinion type steering apparatus.
2. Description of the Related Art
A steering boot covers a ball joint, which is disposed between a steering gear box and a tie rod. Specifically, one of the opposite ends of the steering boot is fastened to a steering-gear-box end, and the other one of the opposite ends of the steering boot is fastened to a tie-rod end. Moreover, the steering boot is disposed in proximity to engine. Accordingly, the ambient temperature around the steering boot is a high temperature relatively. Consequently, air, which is sealed inside the steering boot, expands to deform the steering boot.
FIG. 9 illustrates a side view of a conventional steering boot, which has deformed. As illustrated in the drawing, when the air inside a conventional steering boot 100 expands so that the conventional steering boot 100 expands and then deforms. As a result, the conventional steering boot 100 has come to undulate in a zigzag manner like a letter “S” shape. When the conventional steering boot 100 thus undulates, it might interfere with the built-in ball joint (not shown) or clamps. Accordingly, there might possibly arise such a drawback that the conventional steering boot 100 is damaged. Moreover, the conventional steering boot 100 is made of resin. Consequently, the conventional steering boot 100, which has once undergone undulating deformation, is less likely to recover the original configuration even when being cooled.
Hence, the following measure has been carried out conventionally to inhibit the undulating deformation of steering boot. For example, a steering boot is molded as a configuration whose axial length is longer than that of objective configuration. Then, the thus molded steering boot is subjected to a heat treatment to make it into the objective configuration.
Moreover, Japanese Unexamined Patent Publication (KOKAI) Gazette No. 10-238,629 discloses a conventional steering boot in which the undulating deformation is suppressed. The conventional steering boot set forth in the gazette comprises a major-diameter faster 102, and a bellows. The bellows has three roots, which are numbered starting at the one next to the major-diameter fastener 102 and which are provided with a letter “U”-shaped peripheral groove. The letter “U”-shaped peripheral grooves are dented in the three roots. Accordingly, the portion of the bellows, which is provided with the peripheral grooves, exhibits a higher radial rigidity than the other portion, which is free of the peripheral grooves, does. Consequently, the conventional steering boot set forth in the gazette is less likely to undergo the undulating deformation.
In addition, Japanese Unexamined Patent Publication (KOKAI) Gazette No. 2005-315,364 discloses a steering boot in which a portion making an outer peripheral side of ball joint is made relatively thinner than the other portions are. In this conventional steering boot, the portion making the outer peripheral side of ball joint is compressed relatively by the rising inner pressure, and the other portions are extended relatively thereby. Accordingly, in the bellows of the conventional steering boot, the bending deformation enlarges on the outer peripheral side of ball joint. Consequently, the bending deformation positions the bellows as a whole on the outer peripheral side of ball joint while contracting the bellows. As a result, the conventional steering boot hardly interferes with one of the opposite ends of ball joint.
Moreover, Japanese Unexamined Patent Publication (KOKAI) Gazette No. 2005-315,364 further proposes to make the radii of the crests and roots of the bellows smaller gradually in the direction away from the major-diameter fastener 102 to the minor-diameter fastener 103. In the thus constructed bellows, the closer to the opposite end on the side of the major-diameter fastener 102 is the larger the pressure-receiving radius becomes relatively upon the rise of inner pressure; and the closer to the opposite end on the side of the minor-diameter fastener 103 is the smaller the pressure-receiving radius becomes relatively thereupon. Accordingly, the extending force of the bellows, which is exerted by the rising inner pressure, is larger relatively on the side of the major-diameter fastener 102, and is smaller relatively on the side of the minor-diameter fastener 103. That is, the bellows extends on the side of the major-diameter fastener 102, but contracts on the side of the minor-diameter fastener 103. Consequently, the extension of the bellows on the side of the major-diameter fastener 102 inhibits the portions of the bellows, which are disposed closer to the opposite end on the side of the major-diameter fastener 102, from moving diametrically. As a result, the conventional steering boot can inhibit the interference with one of the opposite ends of ball joint furthermore.
In addition, Japanese Unexamined Patent Publication (KOKAI) Gazette No. 2005-147,297 discloses a steering boot in which the central section of the bellows has a root inside diameter, which is made identical with or smaller than that of the portions on the side of the major-diameter fastener 102; and the central section thereof exhibits a lower radial rigidity than that of the other portions. Namely, this conventional boot comprises a bellows which exhibits an enhanced diametric rigidity on the side of the major-diameter fastener 102, and at the same time an axial rigidity, which is held at the same level as that of the central section of the bellows, on the side of the major-diameter fastener 102. The conventional steering boot can be inhibited from undergoing the undulating deformation by such a relatively simple means as changing the root inside diameter of the bellows. Accordingly, the conventional steering boot needs the man-hour requirement for machining the mold less. Consequently, the conventional steering boot can be manufactured at lower cost. Moreover, the bellows is less likely to deform on the side of the major-diameter fastener 102 because the diametric rigidity is enhanced on the side of the major-diameter fastener 102 while retaining the axial rigidity thereon. As a result, the bellows is less likely to interfere with a clamp, which is disposed around the major-diameter fastener 102, on the side of the major-diameter fastener 102.
However, the conventional method for inhibiting the undulating deformation of steering boot by means of heat treatment requires post processing, such as annealing for removing the residual internal stress from the resulting steering boot. Therefore, the conventional method suffers from the drawback that the man-hour requirements are great.
In the conventional steering boot disclosed in Japanese Unexamined Patent Publication (KOKAI) Gazette No. 10-238,629, it is needed to provide the bellows with the peripheral grooves in order to enhance the rigidity. However, note that the peripheral grooves are irrelevant to the inherent function of bellows. Accordingly, the man-hour requirements for machining a mold for the conventional steering boot have increased. Consequently, the conventional steering boot has suffered from a high manufacturing cost inevitably. Moreover, when providing the bellows with the peripheral grooves, the conventional steering boot has adversely exhibited a degraded rigidity in the expansion/contraction direction of the bellows. As a result, there might arise a probability that, upon the expanding deformation, the part of the bellows, which has undergone the undulating deformation, has been likely to interfere with a clamp, which is fastened to an opposite end of steering gear box.
The conventional steering boot disclosed in Japanese Unexamined Patent Publication (KOKAI) Gazette No. 2005-315,364 has the following problem. That is, since the parts of the bellows, which make the outer peripheral side of ball joint, are thinned out, the thinned-out parts are likely to be damaged when they happen to be disposed in between ball joint and flying ballast upon colliding with flying ballast.
Moreover, in the conventional steering boot disclosed in Japanese Unexamined Patent Publication (KOKAI) Gazette No. 2005-147,297, the undulating deformation is inhibited by making the inside diameter of the bellows' roots smaller around ball joint. Accordingly, it is difficult to inhibit the sections of the bellows, which are disposed away from ball joint, from undergoing the undulating deformation. Consequently, when a ball joint is positioned off from the central section of the bellows, the sections of the bellows, which are disposed away from the ball joint, might possibly undergo the undulating deformation.